1. Field of Invention
The present invention relates to the field of down hole equipment. More specifically, the invention relates to a non-plugging nozzle that has particular usefulness in preventing balling, or packing off in drill bits.
2. Related Art
In the drilling of oil wells, drilling fluid, or mud, provides lubrication and cooling for the drill bit and provides for removal of the cuttings from the well bore. The mud circulates down through a drill string, into the drill bit body, through nozzles positioned at the bottom of the drill bit, and toward the bottom of the well bore. In soft formations, the nozzles are particularly useful because the relatively high pressure mud creates a turbulence within the hole and stirs up formation cuttings facilitating their circulation from the well bore. From the well bore bottom, the mud circulates back to the surface carrying formation cuttings from the well bore. The process of removing the cuttings from the well bore and the efficiency with which it is accomplished is an important factor in determining the rate of penetration of the drill bit and, thus, the efficiency of the drilling. Therefore, increasing the efficiency of the removal of the cuttings increases the drilling efficiency.
Typically, drill bits define voids between the cutting surfaces. Drilling mud and formation cuttings often accumulate within the voids and form a mud ball that becomes impacted. This process, or phenomenon, of accumulation and impaction is generally referred to as "balling" or "packing off." Balling reduces the efficiency of the drilling process because a portion of the cutting energy is consumed when the cutting surfaces act on the impacted mud ball and the mud ball tends to hold weight intended for cutter penetration. Also, the ball can block the flow of fluid to the well bore bottom and impede the removal of cuttings which can often damage the drill bit. Thus, the drill bit should be designed to avoid balling.
One type of drill bit, a polycrystalline diamond compact (PDC) bit, has a plurality, normally at least three, fixed cutting surfaces that extend radially from the axis of the PDC bit, are evenly spaced from one another, and define voids therebetween. The cutting surfaces are positioned so that, as the PDC bit rotates about its axis, the cutting surfaces remove material from the well bottom. Typically, PDC bits include a nozzle directed at each of the cutting surfaces to lubricate, cool, and clean the cutting surface. Periodically, however, one or more of the nozzles often becomes plugged and fails to provide the needed drilling fluid to the associated cutting surface. With one nozzle plugged, the flow is diverted to the other nozzles and cutting blades. Additionally, even when the nozzle is not plugged, the voids between the cutting surfaces may experience balling, or packing off, within the voids. Whether a nozzle is plugged, the drill bit experiences balling, or a combination of these or other mud and flow related problems, the efficiency of the drilling and the rate of penetration is reduced.
Many different nozzles have been created to attempt to increase the efficiency of the mud flow, lubrication, and cleaning of drill bits. Among the prior efforts are nozzles that attempt to produce swirling flows, alter the pressure distribution and turbulence of the flow, or create a cross flow through the center of the drill bit (especially for rotary cone rock bits). However, although many of the previous nozzles improve the efficiency of the drilling operation, additional improvements are needed to further increase the efficiency and lower the cost of production.
One limitation associated with the design of nozzles used for drilling involved the minimum allowable hole diameters which are limited by the size of the particles in the mud. Drilling mud is filtered before being placed in the formation to remove most of the larger particles. However, because the mud circulated into the formation typically still contains relatively large particles, the passageways and nozzle exits commonly have a minimum diameter of about 10/32 inches. Passageways and nozzle exits smaller than this minimum have a tendency to clog. Plugging of the nozzle prevents the desired flow, reduces the efficiency of the process, and may cause additional damage to the drill bit. However, limiting the minimum diameter limits the flexibility of the nozzle design by effectively setting a minimum flow through the hole and limiting the allowable distribution of the nozzle. Accordingly, a non-plugging nozzle that allows the use of smaller holes is desired to improve the efficiency and flexibility of the nozzle.
Thus, despite the use of the prior art features, there remains a need for a non-plugging nozzle that may be used in connection with drill bits and that may accommodate exit holes smaller than those formally possible. Also, there is a need for an anti-clogging, self-cleaning PDC bit that also resists balling.